Implement Circular Queue - EPI

EPI Solution:
https://github.com/epibook/epibook.github.io/blob/master/solutions/java/src/main/java/com/epi/CircularQueueTemplate.java
  public static class Queue<T> {
    private int head = 0, tail = 0, count = 0;
    private Object[] data;

    public Queue(int cap) {
      data = new Object[cap];
    }

    public void enqueue(T x) {
      // Dynamically resize due to data_.size() limit.
      if (count == data.length) {
        // Rearrange elements.
        Collections.rotate(Arrays.asList(data), -head);
        head = 0;
        tail = count;
        data = Arrays.copyOf(data, count << 1);
      }
      // Perform enqueue
      data[tail] = x;
      tail = (tail + 1) % data.length;
      ++count;
    }

    public T dequeue() {
      if (count != 0) {
        --count;
        T ret = (T) data[head];
        head = (head + 1) % data.length;
        return ret;
      }
      throw new RuntimeException("empty queue");
    }

    public int size() {
      return count;
    }
  }

http://oppansource.com/queue-implementation-in-java-using-circular-array/
http://www.java2s.com/Code/Java/Collections-Data-Structure/CircularQueue.htm